1. Field of the Invention
The present invention relates to a heat treating apparatus for applying a heat treatment to an object such as a liquid crystal display (LCD) substrate.
2. Description of the Related Art
In the manufacture of a liquid crystal display (LCD) device, a thin film of, for example, ITO (Indium Tin Oxide) or an electrode pattern is formed in general on the surface of an LCD substrate made of glass. For forming the ITO thin film or electrode pattern, a photolithography technique widely employed in the manufacture of a semiconductor device is used for forming a resist film on the LCD substrate, followed by copying a desired circuit pattern onto the resist film.
To be more specific, an object to be treated, e.g., a rectangular LCD substrate, is washed in a washing device, followed by applying a hydrophobic treatment, i.e., treatment to make the substrate surface hydrophobic, to the LCD substrate in an adhesion treating device. Further, the LCD substrate is cooled in a cooling device, followed by forming a resist film by coating on the LCD substrate in a resist coating device. The resultant resist film is subjected to a baking treatment in a heat treating apparatus, followed by selectively exposing the baked resist film to light in an exposure device so as to copy a desired pattern onto the resist film. Still further, a developing solution is applied to the LCD substrate in a developing device after the exposure to light so as to develop the pattern transferred onto the resist film, followed by washing the excess developing solution with a rinsing solution.
The heat treating apparatus for applying a baking treatment to the resist film formed on the LCD substrate comprises a support plate having the LCD substrate disposed thereon, a heating means such as an electric heater for heating the LCD substrate via the support plate, support pins extending through the support plate to support the LCD substrate, and a lift mechanism for moving said support pins in a vertical direction. Where the heat treating apparatus of the particular construction is used for applying a baking treatment to the resist film formed on the LCD substrate, the heat generation from the heating means is controlled so as to heat the support plate to a predetermined temperature, e.g., 120 to 150.degree. C.
If the support plate is heated to, for example, 120 to 150.degree. C. in the conventional heat treating apparatus, however, the support plate is thermally expanded, leading to variation of the position of the holes in the support plate. It should be noted in this connection that, under room temperature before the heat treatment, the support pins 103 extend through the holes 102 made in the support plate 101 such that these pins 103 are not in contact with the walls defining these holes 102, as shown in FIG. 1A. However, when the support plate 101 is heated to a high temperature during the heat treatment, the thermal expansion of the support plate causes the support pins 103 to be brought into contact with the walls defining the holes 102. As a result, the support pins 103 are inclined when moved though the holes 102, as shown in FIG. 1B. of course, the inclination of these support pins 103 gives detrimental effects to the LCD substrate supported by the support plate 101. The effect given to the LCD substrate by this inclination is increased with increase in the size of the substrate. What should also be noted is that the direct contact between the support pin 103 and the wall defining the hole 102 brings about particle generation, leading to reduction of the yield. These difficulties tend to be rendered more serious with increase in the size of the support plate 101 and with elevation of the heating temperature.
Also known is a heat treating apparatus comprising an air cylinder for driving a shutter member for opening/closing the treating space of the apparatus. In the heat treating apparatus of this type, however, it is difficult to control as desired the clearance formed between a cover member arranged to define a treating space together with the support plate 101 and a shutter member, making it difficult to maintain the clearance at a desired level. As a result, it is impossible to ensure a desired amount of air introduction into the heat treating apparatus, leading to an uneven heating of the LCD substrate and, thus, to a low yield.